The present invention relates to a multichannel pipette with several spigots (“lugs”) for clamping up pipette tips and an ejection equipment for detaching pipette tips from spigots.
Pipettes are used for dosing liquids, notably in medical, biological, biochemical, chemical and other laboratories. The liquids are picked up and delivered in pipette tips through a tip opening. In air cushion pipettes, a displacement equipment for air is integrated into the pipette and communicatingly connected to the pipette tip through a connection hole of the spigot. An air cushion can be dislocated by means of the displacement equipment, so that liquid is sucked into the pipette tip and ejected out from there. The displacement equipment is mostly a cylinder with a piston that can be relocated therein.
The pipette tips are detachably connected to the spigot, so that they can be replaced by a new pipette tip after use. Through this, contaminations are avoided in subsequent dosings. Single use pipette tips made of plastics are available at low cost.
The spigot for holding pipette tips is also designated as “working cone” and is often a conical or cylindrical projection with respect to a casing or another base body. The pipette tip can be clamped up onto the spigot with a suitable seal seat on a plug-on opening. This can happen without touching the pipette tip by pressing the pipette with the spigot into the plug-opening of the pipette tip which is made available in a holder.
In order to avoid contact of the user with the contaminated pipette tips, pipettes have an ejection equipment with a drive device and an ejector. By actuating the drive device, the ejector is dislocated such that it detaches the pipette tip from the spigot without that the user must touch it. The drive device has often a mechanism which must be actuated by means of a button in order to detach the pipette tip from the spigot. Alternatively, the drive device has an electric motor which can be controlled by actuating a button in order to detach the pipette tip from the spigot. This applies in particular for manual pipettes, i.e. pipettes which are can be held and operated by the user with one or both hands in the utilization. In the embodiment as manually driven pipettes, these pipettes have a mechanism for the displacement equipment which is manually drivable by means of a dosing button, and in the embodiment as electronic pipettes an electric drive motor for the displacement equipment which can be controlled by means of an electric dosing button.
Detaching a pipette tip from the spigot can necessitate a significant effort when a pipette tip is to be firmly clamped up on a spigot.
Multichannel pipettes serve for picking up liquid from one or several vessels or to deliver into one or several vessels concomitantly. Multichannel pipettes are often used for the handling of microtiter plates, which have a plurality of vessels in a matrix-like arrangement. For this purpose, multichannel pipettes have several spigots, arranged parallel side by side in a row in the same height, whose through holes are each one connected to a separate displacement equipment or to a common displacement equipment. In adaptation to a frequently used format of microtiter plates with 96 (=8×12) vessels, multichannel pipettes have frequently eight or twelve spigots. The several displacement equipments or the common displacement equipment are connected to a mechanical drive device in a manually driven multichannel pipette, and to an electric drive motor in an electronic multichannel pipette. Further known are multichannel pipettes with an ejector, which squeezes all pipette tips off from the spigot by a straight-lined stop element and has a manually drivable drive mechanism for this purpose. The expense for squeezing off several pipette tips from the spigots of a multichannel pipette is significantly higher than in a single-channel pipette wherein only one pipette tip is squeezed off from one spigot.
Multichannel pipettes are already known in which, in order to reduce the effort for ejecting the pipette tips, an ejector is not realised by a straight-lined stop element, but with a stepped stop element. In these multichannel pipettes, the steps hit the pipette tips one after the other, so that only the force must be applied for ejecting those pipette tips which have contact with steps of the ejector at the same time. The maximum force to be brought up for the ejection of the pipette tips is reduced through this. A stepped stop element results in different plug-on heights of the pipette tips on spigots of a multichannel pipette. With different plug-on heights, not all the pipette tips which are plugged onto the spigots of the multichannel pipette at the same time do reach the bottoms of a microtiter plate.
The document DE 10 2004 003 433 B4, the entire contents of which is incorporated herein by reference, describes a multichannel pipette which reduces the effort for the actuation of the ejection equipment in that it limits the force for clamping the pipette tips onto the spigots. For this purpose, the multichannel pipette has a base body, several spigots projecting from the base body and axially movably mounted on the base body for putting up pipette tips, displacement equipments which are fixedly connected to the spigots, and springs via which the displacement equipments are supported on the base body. A stop is associated to the spring loaded spigots beyond which the spigots protrude axially when they are not loaded towards the spring. An ejection equipment for detaching the pipette tips from the spigots has an ejector associated to the spigots, wherein the spigots and the ejectors are movable relative to each other. The stop may also be the ejector. In addition, the multichannel pipette has a drive device, operatively connected to the ejector and/or the spigots, for relative movement of ejector and spigot.
When the multichannel pipette is being plugged into the plug-in openings of several pipette tips with the spigots, the clamping force is introduced into the springs. When the clamping force exceeds a certain value, the springs are elastically deformed until the pipette tips clamped onto the spigots butt against the stop. As soon as the pipette tips abut on the stop, they cannot be thrust onto the spigots any farther. The clamping force of the pipette tips is limited by this. The springs are dimensioned such, and preloaded if need be, that the pipette tips abut on the stop accurately then when they sit on the spigots with the desired clamping force. The clamping force is determined such that the pipette tips sit and seal securely on the spigots.
The known pipette avoids high clamping forces, which would hamper the ejection of the pipette tips. However, the clamping force which is necessary for a safe seat and the sealing of the pipette tips on the spigots must be overcome in the ejection process. The overall ejection force to be applied is high, because several pipette tips must be squeezed off at the same time.